1. Field of the Invention
The invention relates to color, preferably multicolor, dichroic polarizers and a method for their production. In this type of polarizers the color- and polarizing effect is produced by the dichroic absorption of non-spherical particles, chiefly metallic particles, deposited in glass as a substrate material. The invention relates to the forms of the particles in the substrate material and thus to the form and spectral site of the absorption bands, as well as to a method for the adjustment of the same.
2. Discussion of Background Information
The field of use of the invention is polarizers in the visible, ultraviolet and near infrared spectral region preferably with dichroic absorption bands laterally differently adjusted in a specific manner. Such polarizers are suitable, i.a., for the production of displays.
It is known that uniformly oriented non-spherical particles in substrate materials can lead to dichroic absorption bands. Typical examples are silver, copper, or gold particles in glasses. Oriented spheroid metallic silver particles lead, e.g., in glasses to dichroic absorption bands in the visible, ultraviolet and near infrared spectral region. In the visible spectral region, the dichroic absorption causes a color effect that is dependent on the polarizing direction. In the case of silver particles, it is characteristic thereby that the dichroic behavior is produced by a single absorption band. The absorption band in the visible spectral region can be placed in principle at different points of the visible spectrum, by means of which various color effects can be adjusted. The site of the absorption band maximum in the spectrum is essentially determined thereby by the form of the particles. In the case of ellipsoid particles, the spectral site of the absorption band is determined by the semiaxis ratio of the particles.
There are numerous suggestions that utilize this effect for special applications.
A method for the production of a dichroic polarizer for liquid crystal displays is known from DE 29 27 230 C2 “Method for the production of a polarized glass film, glass film produced accordingly, and use of such a film in liquid crystal displays”. The starting point is an organic or inorganic glass melt into which needle-shaped bodies are introduced and from which a glass film is drawn.
It is known to produce highly polarizing glasses on the basis of phase-separated silver halide-containing glasses in which silver halide particles of the desired size are produced by tempering (U.S. Pat. No. 3,653,863). This is followed by two further steps: First the glass is stretched, extruded, or rolled at temperatures between the upper cooling point and the glass transition temperature in order to endow the silver halide particles with an ellipsoid shape and to orient them in the same direction. Then the glass is exposed to a radiation, e.g., UV radiation. Metallic silver is deposited on the surface of the silver halide particles thereby. These glasses can be adjusted between clear unpolarized and darkened-polarizing, by irradiation.
Furthermore, it is known to temper glass below the cooling point in a reducing atmosphere in order to produce elongated silver particles in a surface layer of the glass of at least 10 μm thickness (U.S. Pat. No. 4,304,584). The production of a glass combined to create a laminate, whereby polarizing and photochromic glass layers are combined and laminated, is described there.
It is known to laminate a metal halide-containing glass with another glass before the deformation process, in order to achieve higher eccentricities of the metal particles (U.S. Pat. No. 4,486,213).
It is known to produce UV polarizers in that the formation of metal particles occurs in a surface layer of glasses by means of a repeated change in the introduction of metal ions and tempering (DE 198 29 970). The result of this is the formation of spherical particles with a certain size distribution. With a subsequent deformation of the glass, spheroid particles of differing size with differing semiaxis ratios are formed.
These methods have in common that submicroscopic, as a rule spherical, foreign phase particles are produced in a substrate matrix, which particles are subsequently deformed in a deformation process and are oriented uniformly in a preferred direction. The resulting dichroic absorption bands of the deformed foreign phase particles are essentially determined by their form and are thus fixed.
Furthermore, it is known that when the substrates are warmed to temperatures near to or above the transformation temperature of the glass, a relaxation of the particles back to the spherical shape occurs. A change in the dichroic absorption is associated with this. Depending on the temperature and duration of their treatment, particles with any desired degree of relaxation between the starting condition and spherical form can be produced. However, the tempering process, whose duration is usually in the range of hours, allows only the monochromatic adjustment of dichroic polarizing glasses to certain colors.
It is known to shorten the relaxation times for the transition of the metal particles from one semiaxis ratio to a smaller one, down to the microsecond range, by using temperatures considerably above the transformation point of the glass (DE 196 42 116). The energy transfer occurs in a structured manner with electron beams. The method additionally allows the absorption band and thus the color effect to be adjusted differently in a specific manner in different lateral regions of the substrate. In this manner flat elements of different colors with lateral dimensions down to far below 100 μm can also be produced.
The principal deficiency of the prior art is that the absorption bands that can be produced, in the case of silver a single band, are always fixed on the band form, which is determined by the form of the particles. More complex band forms cannot be produced.
If it is desired to produce full color by additive color mixing of the primary colors red, green, and blue, however, specific demands must be made on the absorption spectra that cannot be met by the prior art. In order to obtain one of the three primary colors when illuminated by daylight, the two other primary colors must respectively be strongly absorbed. In order, for example, to obtain the colors red or blue respectively when illuminated by daylight, broad absorption bands are required that absorb in the blue and green or red and green spectral region respectively. In order to obtain green, two absorption bands with maxima in the red and blue spectral region are necessary. This lies outside the possibilities offered by the prior art.
For use of the dichroic polarizers for color displays, however, it would be necessary to arrange for small regions with such absorption bands to be closely adjacent, in order to make an additive mixture of the primary colors physiologically effective for the observer.